By way of example, such a linear guide for a coordinate measuring machine is shown in U.S. Pat. No. 6,629,778 B1. FIG. 1 of this document shows such a linear guide in a side illustration, the linear guide likewise including an elongate guide body and a bearing cage, on the inner sides of which fluid pressure bearings are provided. Here, the bearing cage is provided to move along the elongate guide body by way of the fluid pressure bearings. In the embodiment shown therein, the bearing cage includes four plates which are fastened to one another, wherein each plate includes an inner surface facing the guide body, an outer surface facing away from the guide body and side surfaces between the inner surface and the outer surface. For the purposes of forming the bearing cage, each plate is connected to a first other plate in a first end region and to a second other plate in an opposite second end region. With a side surface, the upper plate of the bearing cage in this case abuts against the inner surface of the plate respectively fastened thereto in both the first end region and the second end region. Here, fastening to one another is carried out by screws in each case. By contrast, with the side surface thereof, the lower plate of the bearing cage on one side abuts against the inner surface of a vertical plate fastened thereto. By contrast, the inner surface of this lower plate abuts against a side surface of a vertical place adjoining thereon in the other end region of this lower plate. Here too, the plates respectively fastened to one another are connected by way of screws.
Here, air bearings are used throughout as fluid pressure bearings in the bearing cage, these fluid pressure bearings being separated from the plates of the bearing cage. The relevant air bearings include a membrane which may deform under the pressure of the air. In two of the four plates of the bearing cage, the fastening of the air bearings has a rigid embodiment in the direction perpendicular to the inner surface of the respective plate on which an air bearing is fastened. However, some of these air bearings may carry out rotations. The corresponding axes of rotation are parallel to the plane formed by the inner surface of the respective plate on which the respective air bearings are incorporated. By contrast, air bearings which are fastened by way of springs on the respective inner surfaces of the plates are arranged on the two other plates of the bearing cage, which likewise immediately adjoin one another. As a result of this, each one of the relevant air bearings may carry out a movement in a direction perpendicular to the plane which is formed by the respective inner surface of the associated plates. Moreover, a bearing by means of which the relevant fluid pressure bearings may likewise carry out rotations about axes of rotation relative to the respective plate is additionally provided. The axes of rotation are likewise parallel to the plane formed by the respective inner surface of the plate.
Such a linear guide works very well indeed. However, the production of such a linear guide is relatively complicated on account of the fluid pressure bearings which are to be produced separately.
The prior art has also disclosed linear guides of the aforementioned type, in which the fluid pressure bearing is formed by the plate itself. To this end, the plate substantially has only one hole which is supplied with the fluid (generally air), with the fluid then flowing in a very narrow gap between the inner side of the respective plate and the guide body. A reducer may be provided in the hole in order to limit the flow of the fluid. Here, the peculiarity of such a bearing cage should be considered that of the relevant bearing cage having to be adapted very precisely to the respective elongate guide body. This moreover has as a consequence that the elongate guide body must be manufactured very precisely so that the latter fits to the respective bearing cage.
U.S. Pat. No. 9,109,747 B2 has disclosed a method, by means of which elongate guide bodies may be produced by virtue of four ceramic plates being adhesively bonded to one another at the ends thereof. This renders a comparatively simple production of ceramic guides possible. However, the peculiarity of this method should be considered that of such guides only being able to be produced within relatively rough tolerances.